1. Field of the Invention
The invention is a reciprocating piston mechanism for use in heat engines or in crank driven compressors. The invention may also be classified as a variable stroke, variable crank throw, or free floating piston engine system.
2. Description of Prior Art
Almost all reciprocating systems used in heat engines and compressors today are of the type generally described as four-bar mechanism having a sliding piston member. Piston motion in the four-bar slider mechanism is most commonly estimated from its positional relationship within the engine cylinder relative to the top-dead-center position and is calculated as the sum of the chordal heights generated by the swing of the crankpin and pivotal movement of the connecting rod when measured along the axial center of the cylinder. Therefore, changes in piston velocity and acceleration can only be accomplished by changes in the chordal influencing functions. In the present invention this is accomplished by cyclical changes in the effective crank radius and connecting rod angle.
In engines of the general type to be described an additional link is placed between the crankpin and the main journal of the connecting rod thus creating a five-bar system. The added link is a disc, hereinafter termed the "transfer disc", which is constrained to a pivotal motion thus creating a partially constrained five-bar linkage. I have discovered that the constraining boundaries of these types of systems can be used to vary the crank radius and connecting rod angle, as previously stated, in a manner which is most conducive to the efficient operation of such equipment. With this type of system the effective crank radius can be increased on the downstroke thus improving the mechanical advantage during the power stroke. In a similar manner the effective crank radius is decreased on the upstroke thus decreasing the pumping work during the compression. In this instance the free-floating piston action, which occurs as a result of the pivotal action of the transfer disc, is used to accelerate the final compression which facilitates ignition and propagation of combustion when the engine is operated at lean fuel limit.
The present invention, though similar to the referenced application represents an alternative method of applying constraint to the fifth bar, which in this instance is the transfer disc. In the present invention the constraining mechanism, which is a second crankpin termed "the secondary crankpin", is fixedly attached to the crank arm and therefore is easily balanced by the design proportions of the crank counterbalance. In the referenced application the constraining pin is subject to radial accelerations which can result in the amplification of primary vibration and to increased bending moments and torsional stresses on the crank.
The construction of crank of the present invention is simplified over that of the referenced application by mounting the secondary crankpin on the crank arm adjacent to the primary crankpin and therefore the cost to manufacture this system is less.
In the present invention each throw of the crankshaft contains two crankpins, a primary crankpin and the aforementioned secondary crankpin. The transfer disc is rotatively mounted on the primary crankpin but its motion relative to that of the crankshaft is pivotally controlled within specified limits by the secondary crankpin which works in a slot machined in the transfer disc. The length of the slot in the transfer disc determines the range or boundary for five-bar operation which is the period during which the secondary crankpin is not in contact with either end of the slot and the piston is moving freely under its own momentum. Because the engine depends heavily on inertial loads applied on the reciprocating components for proper operation, it functions most reliably when operated at a constant speed for powering electrical generators and pumping equipment.
The most novel feature of the design is the crankshaft which employs two crankpins. This feature operating in conjunction with the aforementioned transfer disc, allows the piston to accelerate during the terminal period of the compression stroke. The accelerated compression stroke increases the molecular collision rate of the fuel and oxygen particles inducted above the piston thus facilitating ignition and combustion at lean limit conditions which decreases the fuel consumption rate of this type of engine.